A European spacecraft called Rosetta has become the first in history to rendezvous with and orbit a comet, a milestone in space exploration that could reveal valuable clues about how the solar system was created and how it evolved.

On Wednesday, Rosetta and the comet were hurtling side by side at roughly 34,000 miles per hour, locked in a common orbit around the sun, some 250 million miles from Earth, said the Paris-based European...